Process integration of mechanical and/or electrical support features of Microelectromechanical systems (MEMS) devices often present the challenge of scaling the building blocks or fundamental units of the MEMS devices. For example, conventional MEMS devices, such as microbolometer structures, rely on large vias and trenches to support suspended sensor membranes. To achieve mechanical and/or electrical robustness, however, these large vias and trenches are difficult to scale down.
In a conventional approach of manufacturing a support structure for a suspended MEMS device, a large trench is formed in a sacrificial material layer, and then a metal is deposited in the trench. The formation of the trench in the sacrificial material layer, such as a polymer layer, presents challenges during manufacturing processes since polymers are visco-elastic and tend to outgas during thermal and chemical processes. The carbonaceous sacrificial material layer can in turn cause deformation of the trench as well as the metal filament inside. Via deformation may cause structural instability of the support structure. In some extreme cases, via deformation may cause mechanical and electrical detachment of the via from its underlying contact, which may render the MEMS device inoperable. Moreover, in the conventional approach, the support structure having the metal filling may be susceptible to chemical attacks on the sidewalls and the top surface of the support structure during subsequent BEOL (back end of line) processes. These attacks can weaken the support structure and cause electrical and mechanical contact problems.
As dimensions of MEMS structures continue to scale down in size, MEMS device support structures also need to scale down proportionally with the MEMS structures to conserve valuable surface area on a semiconductor wafer, while still being able to uphold the structural integrity of the MEMS structures. Thus, there is a need in the art for high volume manufacturing of robust self-supported MEMS structures.